Real Subband Signal Weighting With Alias Correction

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Solution Overview

Problem

Critical sampling in filter banks leads to aliasing artifacts when amplification factors for neighboring subbands differ, causing audible interferences, and existing solutions either introduce complexity or require long filters, which are computationally expensive and delay-prone.

Innovation Solution

Divide subband filtering into a weighted normal portion and a correction portion, where the correction portion is calculated based on another subband's weighting factor, allowing for shorter filters and reduced aliasing without back-and-forth filtering.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If critical sampling is used in filter banks, then decimation ratio is maximized and computational efficiency is improved, but aliasing artifacts occur when amplification factors for neighboring subbands differ

Engineering Contradiction:

Improvedecimation ratioVSAvoidaliasing artifacts

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The filtering operation is segmented into two distinct parts: a normal filtering portion and a correction portion. The normal portion performs standard subband filtering, while the correction portion specifically addresses aliasing artifacts by processing differences in amplification factors between neighboring subbands. This segmentation allows the system to maintain critical sampling for efficiency while eliminating aliasing through targeted correction.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The aliasing correction is extracted as a separate processing step from the main filtering operation. By identifying and isolating the aliasing components generated by differential amplification of neighboring subbands, the patent applies correction specifically to these extracted artifacts rather than processing the entire signal through long anti-aliasing filters.

Inventive Principle:

Principle #2Taking out (Extraction)

2Object-generated harmful factors

If long filters are used to reduce aliasing, then aliasing artifacts are suppressed, but computational complexity and processing delay increase

Engineering Contradiction:

Improvealiasing artifactsVSAvoidfilter length

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the approach from using long filters with many coefficients to using short filters combined with a correction term that accounts for amplification factor differences. By parameterizing the correction based on the difference between neighboring subband amplification factors, the system achieves aliasing suppression with significantly reduced filter length and computational complexity.

Inventive Principle:

Principle #35Parameter changes

3Object-generated harmful factors

If long filters are used to reduce aliasing, then aliasing artifacts are suppressed, but processing time and energy consumption increase

Engineering Contradiction:

Improvealiasing artifactsVSAvoidprocessing time

Core Design Contradiction:

Object-generated harmful factorsVSLoss of time

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent replaces expensive long filters with cheap short filters combined with a simple correction mechanism. The correction portion uses minimal computational resources by only processing the difference in amplification factors between neighboring subbands, making it a computationally inexpensive solution that effectively suppresses aliasing artifacts.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

4Adaptability or versatility

If amplification factors for neighboring subbands differ, then frequency-selective signal manipulation is achieved, but aliasing artifacts are generated

Engineering Contradiction:

Improvefrequency-selective manipulationVSAvoidaliasing artifacts

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent applies local quality by treating each subband differently based on its specific amplification factor. The correction portion specifically addresses the local issue of aliasing generated at the boundaries between subbands with different amplification factors. By applying correction locally at each subband boundary rather than globally, the system maintains frequency-selective manipulation capability while suppressing aliasing artifacts.

Inventive Principle:

Principle #3Local quality

Data Source

PatentEP2047462B1Device and method for processing a real subband signal for reducing aliasing effects

Publication Date: 2012.10.24 FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV

Figure 1~2
Figure 3A~3B
Figure 3C~3D

AI summary

In order to process a subband signal of a plurality of real subband signals which are a representation of a real discrete-time signal generated by an analysis filter bank, a weighter (10) for weighting a subband signal by a weighting factor determined for the subband signal is provided to obtain a weighted subband signal (11). In addition, a correction term is calculated by a correction term determiner (12), the correction term determiner being implemented to calculate the correction term using at least one other subband signal and using another weighting factor provided for the other subband signal, the two weighting factors differing. The correction term is then combined with the weighted subband signal to obtain a corrected subband signal, resulting in reduced aliasing, even if subband signals are weighted to a different extent.